1. Field of the Invention
The present invention relates to a structure of an artificial electronic retina for an ophthalmological medical apparatus.
2. The Prior Arts
Blindness is the most serious problem that could happen to human eyes. The mechanism of eyesight is very complicated and is still not fully understandable even with the advanced science nowadays. Therefore, the recovery of eyesight has been impossible.
Besides the functions of sensing light and transmitting signals, retina has functions of preliminary identification of the contour of objects by the complicated and precise image processing circuit. For congenital retina degeneration, there is still no effective medical treatment for it. If a patient suffers from retinitis pigmentosa, he or she will have night blindness starting from around 10 to 20 years old and resulted in imperfect eyesight. The patient will become blind around 40 to 50 years old and there is still no effective medical treatment for it. Potential remedies for retinitis pigmentosa include retinal transplantation, gene therapy, neurohormonal treatment and artificial electronic retina. Among these remedies, the artificial electronic retina plays an important role in ophthalmology because of its potential in massive production.
The design for the artificial electronic retina is mainly categorized into epi-retinal device, sub-retinal device, complete layered retinal device and optic nerve encapsulated device. In the epi-retina device, the electric signals are used to stimulate the ganglion cells to generate the action potential. In the sub-retinal device, the electric signals are used to stimulate the light receiving cells to generate the action potential, and to help the light receiving cells to restore their functions. The epi-retinal device and sub-retinal device are developed at a faster pace and the preliminary human experimental results have been obtained in the United States of America. By using the epi-retinal device and the sub-retinal device, the partial eyesight of patients who suffer from retinitis pigmentosa are able to be restored. The ultimate goal of researches for the sub-retinal device in Taiwan is to develop the full-thickness electronic retina. Currently, the in vivo and in vitro tests have been performed to prove that the electronic retina can generate the recordable electrophysiological responses with the stimulation of light.
The artificial electronic retina is a bioelectronic device in which the electronic photosensitive elements are used to replace the retinal photosensitive cells, and the electronic photosensitive elements can stimulate the remnant optic nerve cells. Therefore, the eyesight can be restored by the electronic signals induced by the transmitted light. Similar devices can be implanted in the cerebrum to stimulate the cerebral cortex to generate eyesight. However, the eyesight system is complicated and huge, and its mechanism is still not fully understandable. Currently, the implantable artificial electronic retina is being emphasized the most in research and development.
The epi-retinal device is currently being developed the most successfully. The remnant ganglion cells of a patient suffered from retinitis pigmentosa are electrically stimulated by the arrays of microelectrodes disposed on the retina (i.e. by the vitreous body). The electrodes are simply the stimulating devices, and the signals and power supply are transmitted to the electrodes directly or indirectly via the wires, the infrared rays or the radio-frequency electric waves. The in vitro electronic photosensitive elements (e.g. CCD) can be incorporated with the suitable lens and with the integrated electronic visual circuits to form a device similar to the glasses. The signals and power supply are output simultaneously and are transmitted to the multiple arrays of microelectrodes on the retina. The epi-retinal device is used by many research institutions because it can be straightforwardly designed, developed and manufactured, and can be tested in vivo more easily.
The sub-retinal device can be used to replace the photosensitive cells on the ectoretina, and its design is simple. Because the sub-retinal device is disposed under the retina, it has the advantage that it is easy to be fixed. Furthermore, most retinal diseases are located on the ectoretina instead of the entorretina, and thereby the design of the sub-retinal device is suitable for applying to the clinical diseases. For patients suffered from retinal detachment, even though the retina can be attached back after a successful surgery, the photosensitive cells are usually dead and the eyesight cannot be restored. The sub-retinal device is capable of replacing the damaged photosensitive cells.
The sub-retinal device is used with the corresponding electronic visual circuits to simulate the collaborated functions of the photosensitive cells, horizontal cells, bipolar cells, amacrine cells and ganglion cells progressively. The sub-retinal device can be designed according to the various retinal diseases.
As humans are exploring and trying to comprehend the visual mechanism of the retina, the artificial electronic retina will be used for simulating the functions of the full-thickness retina in the future based on the improvement made on the research. Therefore, the problems of the retinal diseases can be solved, and even the healthy retina can be replaced, and inconceivable eyesight can be developed. The artificial electronic retina has the commercial, industrial and military potential, and is a major project developed by the advanced countries.
Currently, an artificial electronic retina comprises an array of photoelectric units composed of a plurality of electronic photosensitive elements and a plurality of microelectrodes. One microelectrode of each photoelectric unit is electrically connected to one electronic photosensitive element. Typically, the microelectrode is disposed at the center of the electronic photosensitive element, and an electronic circuit is disposed near the circumference of the electronic photosensitive element. The electronic photosensitive element is similar to the CMOS (complementary metal-oxide-semiconductor) or CCD (charge-coupled device) of the digital camera. After the artificial electronic retina is installed in the eyeball, an electric current is conducted through the array of microelectrodes to stimulate the nerve cells and to activate the electronic photosensitive elements, and thereby the images of light are formed on the photosensitive area of the electronic photosensitive elements. The electric current is then flowed back to the electronic circuits. Based on theories and practices, the output power of the microelectrodes is directly proportional to the effects of stimulating the nerve cells and activating the electronic photosensitive elements. Because the bigger the output power, the bigger the size of the microelectrodes is, so that more areas of the electronic photosensitive elements are covered by the microelectrodes. As a result, the photosensitive efficiency is reduced. Therefore, the input and output power of electric current conducted through the conventional artificial electronic retina cannot be enhanced by increasing the size of the microelectrodes.